The Britain-based Syrian Observatory for Human Rights said it was unclear who controlled the Jafra oil field and nearby Conoco gas field in rural Deir al-Zor, but that both sides in the clashes had sustained casualties in the fighting.

Also in Deir al-Zor, the village of Tibni saw similar clashes that pitted ISIS against the Nusra Front and Islamist allies, with casualties reported on both sides.

The clashes over the oil facilities followed the takeover by the Islamic State of Iraq and Greater Syria of a strategic village, Busaira, which overlooks several villages, the town of Mayadin and several oil fields, the Observatory added.

The man’s fellow tribesmen engaged in a firefight with the Nusra members, while other members of the tribe remained loyal to Nusra, which they have joined during Syria’s uprising.

The clashes killed seven Nusra members, including a commander and its explosives expert for Deir al-Zor province, the Observatory said.

Two of the tribesmen were killed, and 18 Nusra fighters were taken prisoner, it added.

In rural Hassakeh province, a Libyan member of ISIS was killed in fighting with the Nusra Front and Islamist allies, the Observatory said. Meanwhile, ISIS militants clashed with the Kurdish YPG militia elsewhere in the province, with both sides suffering casualties.